Method Of And Molten Metal Feeder For Continuous Casting

ABSTRACT

The invention provides a feeder for delivery of molten metal into a mold formed between confronting casting surfaces of a continuous casting machine. The feeder comprises a projecting nozzle tip having at least a lower wall provided with a molten metal-contacting inner surface, a generally flat outer surface and an end surface at an outer extremity of the tip extending between the inner and outer surface. The inner surface is generally flat and preferably slopes towards the outer surface considered in a direction moving towards the extremity of the tip at an angle of slope of no more than 8 degrees. The end surface is generally flat and extends from the inner surface to the outer surface at an acute angle of less than 88°, e.g. in the range of 15 to 80 degrees, relative to the inner surface in a direction away from the extremity of the tip. The feeder casts a metal sheet article having reduced surface defects caused by rupture of the metal oxide during casting.

TECHNICAL FIELD

This invention relates to the continuous casting of molten metals,preferably aluminum and aluminum alloys. More particularly, theinvention relates to a method of introducing the molten metal into thecasting cavity of a continuous caster and the design of a metal feederused for this purpose.

BACKGROUND ART

Continuous casting of metals has been carried out for many years, e.g.by using a twin belt caster, twin roll caster or rotating block caster.Continuous casters of this kind usually have a horizontal, or slightlydownwardly-sloping, casting cavity formed between two confronting andcontinuously rotating casting surfaces. The molten metal is introducedinto one end of the casting cavity and it is cooled and solidified as itis drawn through the casting cavity by the rotating casting surfaces. Acast ingot, slab or strip of solidified metal emerges from the castingcavity at the opposite end.

Molten metal is introduced into the casting cavity by some form ofmolten metal feeder that introduces a stream of molten metal between thecasting surfaces. The feeder may be in the form of an open toppedtrough, in which molten metal is directed by means of an open spout orchannel into the casting cavity (referred to as “pool feeding”), or morepreferably by means of a nozzle which encloses and confines the moltenmetal until it emerges from a tip at the extreme end of the nozzle.

As-cast ingots produced by both DC (direct chill) and continuous stripcasters produce metal slabs or strips having surface defects of variouskinds. In DC casting such surface defects are often removed by means of“scalping” (i.e. removing a thin surface layer from the cast article).However, in continuous strip casting, scalping may not be practical oreconomical and it is desirable to provide an article at the outsethaving a minimum of surface defects.

Surface defects may be produced by a variety of mechanisms, includingreaction with the refractory materials of the metal delivery system andlocalized cooling non-uniformities, and many improvements have been madeto reduce the size and number of such defects.

Another common mechanism involves entrainment of surface oxides thatform “cold shuts”. Such defects arise from the inevitable surface oxidesthat form on the meniscus surface of the molten metal where it exits themetal feeder to contact the moving casting surface. As the meniscus isdragged along by the moving casting surface, the oxide film becomesstrained and breaks, causing relatively large and visible surfacedefects of an irregular nature. This not only affects the appearance ofthe cast article, but also can introduce structural weaknesses thatcause rollability problems. The defects are particularly critical insurface critical applications such as foil stock, can stock andautomotive sheet, and can limit the speed of casting.

There are various prior references disclosing feeder design and methodsof metal introduction into a continuous casting cavity, e.g. U.S. Pat.No. 5,636,681 which issued on Jun. 10, 1997, and U.S. Pat. No. 6,725,904which issued on Apr. 27, 2004. These patents disclose feeder designsthat are intended to produce non-turbulent metal flow into the castingcavity.

European Patent No. EP 0 962 271 B1, which was granted on Dec. 17, 2003to Hazeleft Strip-Casting Corporation (inventor Valerie G. Kagan)discloses a belt casting apparatus with a metal delivery device that“pours” the metal onto a belt. The tip of the delivery device is spaceda distance away from the surface of the belt and it terminates at an endsurface disposed at right angles to the metal-contacting inner surfaceof the delivery device.

U.S. Pat. No. 4,648,438 which issued on Mar. 10, 1987 to HazelettStrip-Casting Corporation (inventor Robert W. Hazelett, et al.)discloses a belt caster and metal delivery device in which the end ofthe tip is “squared” and is arranged at right angles to the castingsurface.

The following are examples of strip casters having tips in which theinterior of the tip is tapered in the direction of the tip:

U.S. Pat. No. 3,774,670 which issused on Nov. 27, 1973 to Prolizenz AG(inventor Ivan Gyongyos); U.S. Pat. No. 5,660,757 which issued on Aug.26, 1997 to Hunter Engineering Co., Inc. (inventor Denis M. Smith); andU.S. Pat. No. 6,173,755 which issued on Jan. 16, 2001 to AluminumCompany of America (inventor Nai-Yi Li, et al.).

DISCLOSURE OF THE INVENTION

An object of the present invention is to improve the continuous castingof molten metal, especially molten aluminum and its alloys, particularlywith a view to reducing surface defects of the cast article and moreparticularly to reduce the incidence of oxide incorporation into thecast surface.

According to one aspect of the present invention, there is provided afeeder for delivery of molten metal into a mold formed betweenconfronting casting surfaces of a continuous casting machine. The feedercomprises a nozzle having a projecting tip including at least one wallprovided with a molten-metal-contacting inner surface, an outer surface,and an end surface at an outer extremity of the tip extending betweenthe inner and outer surfaces. The inner surface and the end surfaceinterconnect at a line and form an included angle of less than 88°, andthe wall of the nozzle has a thickness adjacent to the line in the rangeof 0.5 to 3 mm.

According to another embodiment, there is provided a continuous castingmachine comprising a pair of endless casting surfaces confronting eachother across a casting cavity, means for moving the casting surfaces inthe same direction at the same speed, and a feeder for introducingmolten metal into the casting cavity at one end of the cavity. Thefeeder comprises a nozzle having a projecting tip including at least onewall provided with a molten-metal-contacting inner surface, an outersurface, and an end surface at an outer extremity of the tip extendingbetween the inner and outer surfaces. The inner surface and the endsurface interconnect at a line and form an included angle of less than88 degrees. The wall has a thickness adjacent to the line in the rangeof 0.5 to 3 mm, and the line is positioned during casting at a spacingfrom an adjacent casting surface within the range of 0.5 to 3 mm.

According to yet another embodiment of the invention, there is provideda process of continuous strip casting a molten metal to form a castmetal strip article. The process comprises feeding a molten metal whichdevelops an oxide layer when in contact with air from a nozzle having aprojecting nozzle tip onto at least one moving casting surface such thatthe metal forms a meniscus having a surface coating of metal oxidebetween an extremity of the tip and the casting surface. The metal isfed from a tip having a wall provided with an inner surface and an endsurface that interconnect at a line and form an included angle of lessthan 88 degrees. The wall has a thickness adjacent to the line in therange of 0.5 to 3 mm. The tip is positioned during casting such that thespacing of the line from an adjacent casting surface is within the rangeof 0.5 to 3 mm.

The present invention is concerned with obtaining a continuously caststrip article of good surface quality. As the inventors obtainedimprovements in surface quality by making general improvements to thecasting technique and apparatus, they noticed the presence of periodicsurface striations extending across the cast article at right angles tothe direction of casting. The inventors found that these striations weredue, at least in part, to oscillations of the meniscus formed betweenthe casting tip and the casting surface. When casting reactive metals,such as aluminum, the meniscus is coated with a layer of metal oxide andthe oscillation of the meniscus can cause this to break. The underlyingmetal thus exposed rapidly grows a new layer of oxide upon reaction withair, but the break forms a visible defect in the surface of the castproduct as the oxide layer is drawn onto the casting surface. It istheorized that meniscus oscillations are inherent in continuous casters,at least in belt casters used for casting aluminum and its alloys, aswell as other reactive metals, and that they cannot be entirelyeliminated. The inventors therefore took another approach, i.e. ofincreasing the uniformity of the oscillations to produce a cast articlehaving small, regularly spaced striations that do not manifestthemselves as surface defects because of their regular and fineappearance. In particular, it was found that an oscillation of themeniscus of at least 50 Hertz, e.g. in the range of 50 to 200 Herz, wasrequired to impart an acceptable appearance to the cast product.

The meniscus tends to oscillate at right angles to its surface, i.e. ittends to become more rounded and then less rounded in the regionextending from the nozzle to the casting surface with each such cyclerepresenting one oscillation.

The inventors found that the frequency of the meniscus oscillations canbe affected by various parameters, e.g. the application of externalforces, such as pneumatic pressure in the small gap between the nozzleand the casting belt, and the application of a varying magnetic field inthe area of the meniscus. However, the inventors found that the mosteffective way to increase the frequency of oscillation is by improvingthe design and placement of the nozzle used for injecting the moltenmetal onto the casting surface.

With regard to the design of the casting nozzle, the conventional nozzleemploys a pair of projecting walls that define a molten metal channelbetween confronting inner metal-contacting surfaces. The channel has anexit at the tip of the nozzle where the projecting walls terminate at aflat end surface that extends at right angles to the innermetal-contacting surfaces. The walls also have outer surfaces that inuse extend along the casting surfaces with a small gap. Using this typeof nozzle, it was noticed that not only was the frequency of oscillationof the meniscus slow and erratic, but the oscillations bring the metalinto contact with the end surfaces of the nozzle walls, causing oxidewhiskers to form and build up, thereby causing further sticking andinterference with the oscillations. The inventors found that this effectcould be minimized or eliminated by “cutting-back” the end surface by afew degrees or more. This means that the end surface is caused to slopein a rearward direction from the line of contact with the innermetal-contacting surface to form an included angle (the angle within thematerial of the nozzle wall) of less than 88 degrees, more preferably 85degrees or less, even more preferably 80 degrees or less, and mostpreferably 75 degrees or less. The minimum angle is preferably 15degrees, because a smaller angle may be currently impractical forconstructing the nozzle (although the desirable effect would still beapparent if the constructional limitations could be overcome). A moredesirable lower limit for the cut-back angle is 30 degrees. An even morepreferred lower limit is 45 degrees. Most preferably, the end surface ofthe nozzle wall is flat along its full length, i.e. from theintersections with the inner and outer walls, and from side to sideacross the nozzle. This has the advantage of making the striations moreregular, particularly across the width of the casting cavity.

The line of contact mentioned above (the apex of the included angle)forms a so-called “take-off point” for the meniscus, i.e. the point atwhich the molten metal loses contact with the nozzle and is brieflysupported by surface tension before contacting the casting surface. Itis necessary to provide such a line (i.e. an abrupt change of directionwhere generally planar surfaces meet at an acute angle). Withoutlimitation as to the theory of operation of the invention, it appearsthat the line and the acute angle at this position fixes the point ofmetal departure from the tip so that it does not wander onto the endface of the nozzle wall. Oscillations of the metal instead appear to belocalized at the take-off line where they break the oxide layer on aregular and frequent basis as the metal leaves the tip, thereby causingregular and fine striations in the final product.

Again without limitation as to theory, it seems that the amplitude ofthe meniscus oscillations increases with casting speed (i.e. the speedof the casting belt). A greater amplitude of the oscillations increasesthe risk of meniscus “wander” onto the end face of the nozzle, so the“cut-back” angle may desirably be decreased as the casting speedincreases (i.e. the angle of the end surface with the inner surfaceshould desirably be made smaller, e.g. within the range of 15 to 80degrees). For fast casting, the angle should preferably be made nolarger than 75 degrees, and 70 degrees or even 65 degrees is a morepreferred upper limit.

Ideally, the meniscus should be caused to oscillate at a frequency of 50herz to about 200 Herz at least for aluminum and aluminum alloys. Therange of frequencies depends on physical properties of the metal, e.g.density, viscosity and surface tension, but only for significant changesin these properties. The variation among aluminum alloys is quite minor,but a change of base metal (e.g. aluminum to copper) may producesignificant changes that affect the oscillations more noticeably.

In the present invention, it is found that the spacing between the“take-off point” and the casting surface should be quite specific. If itbecomes too large, it is difficult or impossible to maintain a stablemeniscus as it may “wander” onto the end wall of the tip and the metalmay run back under the tip of the nozzle. The flow characteristicschange to become more like pouring a liquid rather than casting atspeed. However, the spacing should be large enough to allow a meniscusto form between the take-off point and the casting surface. The minimumdistance is controlled by restrictions placed on the tip by methods ofconstruction and the need for the tip to be spaced slightly from thecasting surface. The preferred spacing (take-off line to castingsurface) is about 1 mm+0.5 mm. However, the invention is effective withnormal nozzle wall thicknesses (usually about 1 mm or 1/32 inch) and aspacing up to about 3 mm.

The metal can be fed into a closed nozzle or to an open-topped nozzlefrom a conventional head box or tundish. The present invention may beused with both types of nozzle, but a closed nozzle is preferred.

When the nozzle is of the closed type, the two walls forming the nozzlemay be flat and parallel throughout their length, or they may be“flared” or “divergent” at the end, i.e. with the walls adjacent to themetal delivery end bending outwardly at an angle of usually no greaterthan about 8 degrees. This allows the walls to converge towards thecasting surfaces by a small angle at the extreme end of the tip.

The present invention may be used with both horizontal and verticalcontinuous casting machines, e.g. twin-belt casters, revolving blockcasters and even twin-roll casters (twin-roll casters are preferablyoperated at high speed when the invention is employed).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partly in cross-section, of a twin-belt caster(without metal feed apparatus) of a type with which the presentinvention may be employed;

FIG. 2 is a cross-section of a metal feeder and adjacent parts of atwin-belt caster of a type with which the present invention may beemployed;

FIG. 3 is a cross-section of a part of a prior art nozzle and anadjacent casting belt and molten metal flow, showing the development ofa metal meniscus;

FIG. 4 is a view similar to FIG. 3, but showing a part of a nozzle inaccordance with the present invention;

FIG. 5 is a top plan view of a test device used in the Example describedbelow;

FIG. 6 is a cross-sectional view of the test device of FIG. 5;

FIGS. 7A, 7B, 7C, and 7D show cross-sections of tips used in the Example1 described below;

FIG. 8 shows a macrophotograph of the surface of an aluminum alloy stripcast with a prior art nozzle having an angle between inner surface andend surface of 93 degrees;

FIG. 9 shows a macrophotograph of the surface of an aluminum alloy stripcast with a nozzle in accordance with the present invention having anangle between inner surface and end surface of 88 degrees;

FIG. 10 shows a macrophotograph of the surface of an aluminum alloystrip cast with a nozzle in accordance with the present invention havingan angle between inner surface and end surface of 78 degrees;

FIG. 11 shows a macrophotograph of the surface of an aluminum alloystrip cast with a nozzle in accordance with the present invention havingan angle between inner surface and end surface of 48 degrees; and

FIG. 12 shows a macrophotograph of the surface of an aluminum alloystrip cast with a nozzle in accordance with the present invention havingan angle between inner surface and end surface of 33 degrees.

BEST MODES FOR CARRYING OUT THE INVENTION

As noted above, continuous casting of metals to form strip articles(often referred to as sheets, plates, slabs, ingots, billets, layers,etc.) has been carried out for many years and in many different types ofcontinuous casting machines. For example, a twin-belt caster isdisclosed in detail in U.S. Pat. No. 4,061,177 which issued on Dec. 6,1977 to Alcan Research and Development Limited (inventor Olivo GiuseppeSivilotti), and casting machines of this kind (as well as others) aresuitable for carrying out the present invention. The disclosure of thispatent is incorporated herein by reference, and a brief and simplifieddescription is provided below.

The illustrated twin belt caster 10 has upper and lower endless rotatingmetal belts 12 and 14 arranged so that closely spaced moving confrontingcasting surfaces 16, 18 of the belts are disposed essentially parallelto each other through a region where they define a casting cavity(casting mold) 20 from a cavity entrance 21 to a cavity exit 22. Thebelts are guided as they rotate through suitable oval or otherwiselooped return paths between the entrance and the exit of the castingcavity. The upper belt 12 passes around a cylindrical driving roll 24and then travels along an upper path where it may be further supported,if desired, by rows of idler rollers or the like (not shown), and thenaround a semi-cylindrical bearing 25. The lower belt follows anessentially identical but mirror image path including a drive roll 26and a semi-cylindrical bearing 27 similar to the bearing locatedimmediately above. Molten metal is introduced into the casting cavity bya feeder 30 (not shown in FIG. 1, but illustrated in FIG. 2)incorporating a nozzle 32 having a projecting tip 34 provided with amolten metal outlet 35 at the outer extremity (extreme end) 36 of thetip. Hence, molten metal enters the apparatus from the feeder 30 in thedirection shown by arrow A (FIG. 1), the metal solidifies within thecasting cavity 20 and a cast strip article emerges from the apparatus atthe exit of the casting cavity in the direction of arrow B as shown. Thereverse (inner) surfaces 17, 19 of the casting belt are generally cooledby means of jets of cooling water, e.g. as shown at 23.

FIG. 2 shows an enlargement of the end of the caster adjacent to theentrance 21 of the casting cavity 20. The belts 12 and 14 are shown indash-dot lines. As previously noted, the apparatus is provided with amolten metal feeder 30 which may be of the type disclosed, for example,in U.S. Pat. No. 5,636,681 issued on Jun. 10, 1997 to AlcanInternational Limited (the disclosure of which is incorporated herein byreference). The feeder 30 comprises top and bottom nozzle mounts 38which hold metal delivery nozzle 32 in place so that its tip 34 projectsbetween the two moving belts 12 and 14 of the belt caster. The mounts 38are bolted to the caster structure (not shown) and support the nozzle 32such that an upstream opening 40 can mate with a similar opening in atundish or feed-box (not shown) used to feed the caster with moltenmetal. A resilient refractory seal (also not shown) is used betweenupstream faces 41 of the nozzle and the tundish or feed-box. The nozzle32 is fabricated from refractory materials, for example as described inU.S. Pat. No. 5,636,681, and the tip 34 has a slightly divergent shapeas shown. Spacers 46, in the form or wire mesh or metal strips, areprovided between the outer surfaces of the nozzle and the adjacentcasting belts to maintain a fixed and controlled spacing between thenozzle and belts. The nozzle includes refractory walls 53 that haveinner molten-metal-contacting surfaces 55 confronting each other acrossa molten-metal-conveying channel 50 leading from the upstream opening tothe metal outlet 35. The walls have end surfaces 56 that interconnectwith the inner surfaces 55 at lines 65. The walls also have outersurfaces 54 that confront the casting belts 12 and 14.

The present invention is primarily concerned with the delivery of moltenmetal into the casting cavity in the region of the nozzle tip 34. Thisis explained in more detail with reference to FIGS. 3 and 4.

FIG. 3 shows a conventional nozzle tip 34 in which only the lower wall53 of the tip is shown adjacent the lower casting belt 14. The upperwall of the tip and the upper casting belt can be visualized as mirrorimages of the lower parts. The illustrated tip has an outer surface 54extending generally parallel to the surface of the adjacent casting belt14, a molten-metal-contacting inner surface 55, and a narrow end surface56 that is disposed at right angles to the inner surface 55 of the tip(as indicated by the small rectangle). In the delivery and casting ofmolten metals, a meniscus 58 (i.e. an unsupported metal surface) bridgesthe gap between the nozzle tip 34 and the adjacent casting belt 14. Forreactive metals (i.e. metals that spontaneously form an oxide layer whenin contact with air) such as aluminum and its alloys, the meniscus iscovered by an oxide layer 60. As the belt 14 moves through the castingcavity, the oxide layer 60 is drawn along by the belt by friction and issubject to stress in the region of the meniscus. It is found that theoxide layer on the meniscus will periodically rupture and the exposedmetal will instantly form a new layer of oxide. The resulting oxidebreakage and re-growth causes surface defects in the cast article. Theinventors of the present invention have found that the effect of theinevitable oxide rupture on surface quality can be reduced or minimizedby ensuring that the oxide membrane ruptures frequently and in acontrolled manner rather than randomly.

In particular, the inventors have found that by causing the meniscus tofreely oscillate at a controllable frequency of at least 50 Hz, theeffect of oxide layer ruptures is controlled and reduced. It has beenfound that a nozzle tip designed and used in accordance with the presentinvention, e.g. as shown in FIG. 4, will allow such regular oscillationsand oxide rupture to occur. In this tip, angle α (referred to as the“cut-back angle” and also as the “included angle”) between the innersurface 55 and the end surface 56 is an acute angle less than 88°,preferably between 15 and 85 degrees, more preferably between 15 and80°, more preferably between 30 and 80 degrees, and even more preferablybetween 30 to 75°. When such an angle is employed, the meniscus 58 isfree to oscillate, and, absent any outside influences, takes on a“natural” frequency determined by the physical properties of the moltenmetal, the contact friction between the molten metal and the movingsubstrate (casting belt) and the spacing of the tip to belt distance(spacing “S” shown in FIG. 4). The use of the acute cut-back angle α, incombination with a precisely defined spacing S of tip to belt, meansthat the geometry of the meniscus is reliably controlled between thecasting surface 61 of the casting belt 12 and the line of intersection65 (referred to as the “take-off point” or “take-off line”) between theinner surface 55 and the end surface 56 of the nozzle tip, so that thefrequency of oscillation is stable. The use of the acute cut-back angleα ensures that the final point of contact between the molten metal andthe nozzle is confined to a fixed position on the tip, namely the lineof intersection 65. At this point, the molten metal surface transfersfrom a supported condition (supported by the nozzle) to an unsupportedcondition (in the form of a meniscus) and the oxide film on the metalsurface is repetitively ruptured along this line as the meniscusoscillates. The oxide rupture has the same regular frequency as thefrequency of oscillation and takes place in small and regular breaks,thus creating regular and minimal defects on the metal surface.

If the cut-back angle α is not acute (e.g. if it is 90 degrees as in aconventional nozzle tip), the meniscus 58 can touch the end surface 56of the tip during oscillation.

This rapidly forms oxide whiskers on the end surface of the tip and thisin turn causes adherence of the meniscus to the end surface 56 below theline of intersection 65. This adhesion is variable and prevents regularand free oscillations of the meniscus from occurring. The breaks in theoxide layer are consequently irregular and delayed and the resultingsurface defects are larger.

The amplitude of the meniscus oscillations appears to be somewhatcasting speed related, i.e. larger amplitudes are encountered at highercasting speeds. As larger amplitudes can result in the meniscus beingmore difficult to fix on the nozzle, it is desirable to reduce the angleα at higher casting speeds and an angle no larger than 75 degrees isusually desirable for high casting speeds. On the other hand, if the cutback angle is less than 15 degrees, it becomes difficult to construct anozzle tip having the requisite stiffness and strength properties.

The spacing S (which is the distance between the “take-off point” 65 andthe casting surface 61 of the casting belt at the point where themeniscus contacts the surface) affects the performance of the castingprocess. For most alloys and casting operations, the spacing S should bein the range of 0.5 to 3.0 mm. The spacing S includes the thickness ofthe lower wall 53 at the tip, and so this thickness must necessarilyalso be within the range of 0.5 to 3.0 mm. The most preferred distancefor spacing S is 1±0.5 mm. This can be achieved, for example, by makingthe sidewall 53 from an alumina-silicate fiberboard (e.g. Fiberfrax®)having a thickness of 1 mm at the tip that is slightly compressed with arigidizer. As the material is slightly compressed and changes inthickness slightly during use due to thermal expansion, the spacing Scan be maintained at about 1 mm with a slight gap forms between thesidewall 53 and the casting surface. The indicated material hassufficient strength and rigidity despite its narrow thickness, anddesirably it also relatively low thermal conductivity.

The invention is illustrated in further detail with reference to thefollowing Examples, which are not intended to be limiting of the scopeof the invention.

EXAMPLE 1

The effects of different feeder tip angles were investigated on a singlemold plane (water cooled) utilizing an open-topped box with a slidingbottom, to simulate the metal flow conditions from a stationary feedertip onto a moving water cooled belt. The apparatus employed is shownschematically in FIG. 5 (plan view) and FIG. 6 (vertical longitudinalcross-section).

The metal was poured into a box 70 and a bottom plate 71 was pulledhorizontally at predetermined speeds and molten metal temperatures,allowing the metal 75 to flow from an end 72 of the moving bottom plateonto a sheet steel mold 73, where it solidified progressively towardsthe moving bottom plate. The moving bottom plate (forming a thin slide)was made of the same material as the feeder tips used for continuouscasting, and the right hand end was changed in geometry as shown inFIGS. 7A to 7D to study the effects of such changes on the solidifiedmetal, such as meniscus break lines and other ingot surface defects. Thespeed of extracting the bottom plate was varied to simulate differentmetal flow rates and conditions of the tip to the mold surface. Thegeometry of FIG. 7A corresponds to the present invention, having a cutback angle of 75 degrees. FIG. 7B has a cut back angle of 120 degrees,i.e. outside the present invention. FIG. 7C has a compound surface butthe angle at the inner corner (“take off point”) is 120 degrees. Thesecond angle does not affect the meniscus because it does not form atake-off point. FIG. 7D has a curved outer surface and there is as aresult no clear inner corner or “take off point”. All conditions inFIGS. 7B, 7C, and 7D resulted in undesirable oxide breaks at thesolidification juncture, but the conditions of FIG. 7A, an undercut tipangle of 75° angle, gave good results. For the same design as in FIG.7A, the undercut angle was changed to 60 and 30°, all with good results,attained by the sharp upper edge shown in FIG. 7A.

EXAMPLE 2

A series of casts were performed in a pilot scale belt caster usingmetal delivery nozzles having various cut-back angles. Casts were madeon copper belts using aluminum alloy AA5754 cast 10 mm thick cast at aspeed of 8 to 10 meters/minute.

The surface of the as cast strip was observed and photographed. Theresults are shown in FIGS. 8 to 12 and are summarized in Table 1 below.TABLE 1 Cut back angle Figure Number Observation 93 degrees 8 Severeoxide banding or folds irregularly spaced about 30 mm apart 88 degrees 9Oxide banding or folds irregularly spaced about 30 mm apart 78 degrees10 Regular fine banding about 1 mm spacing 48 degrees 11 Regular finebanding about 1 mm spacing 33 degrees 12 Regular fine banding about 1 mmspacing

Cut back angles of 93 and 88 degrees are outside the range of angles ofthe invention and the sheet cast using tips at such angles exhibitunacceptable oxide folds or banding. A spacing of 30 mm, typical of suchbands, corresponds to a frequency of about 4 to 6 Hz. Cut back anglesless than 88 degrees show an absence of such heavy bands, but displayfiner more regular surface marks with spacings of about 1 mm,corresponding to a frequency of over 100 Hz.

1. A feeder for delivery of molten metal into a mold formed betweenconfronting casting surfaces of a continuous casting machine, the feedercomprising: a nozzle having a projecting tip including at least one wallprovided with a molten-metal-contacting inner surface, an outer surface,and an end surface at an outer extremity of the tip extending betweenthe inner and outer surfaces, characterized in that the inner surfaceand the end surface interconnect at a line and form an included angle ofless than 88°, and said at least one wall has a thickness adjacent tosaid line in the range of 0.5 to 3 mm.
 2. A feeder according to claim 1,characterized in that said included angle is in the range of 15 to 85degrees.
 3. A feeder according to claim 1, characterized in that saidincluded angle is in the range of 15 to 80 degrees.
 4. A feederaccording to claim 3, characterized in that said included angle is inthe range of 15 to 75 degrees.
 5. A feeder according to claim 3,characterized in that said included angle is selected from a range of 30to 70 degrees.
 6. A feeder according to claim 1, characterized in thatsaid thickness is 1±0.5 mm.
 7. A feeder according to claim 3,characterized in that the tip has two of said walls aligned with eachother with said metal-contacting inner surfaces confronting each otheracross a metal-conveying channel.
 8. A feeder according to claim 7,characterized in that said walls of said tip diverge from each other ina direction extending towards said outer extremity.
 9. A feederaccording to claim 8, characterized in that said walls diverge from alongitudinal axis of the tip at an angle of about 8 degrees.
 10. Acontinuous casting machine, comprising: a pair of endless castingsurfaces confronting each other across a casting cavity; a means formoving the casting surfaces in the same direction at the same speed; anda feeder for introducing molten metal into said casting cavity at oneend of said cavity; wherein said feeder comprises a nozzle having aprojecting tip including at least one wall provided with amolten-metal-contacting inner surface, an outer surface, and an endsurface at an outer extremity of the tip extending between the inner andouter surfaces, characterized in that said inner surface and said endsurface interconnect at a line and form an included angle of less than88 degrees, said at least one wall has a thickness adjacent to said linein the range of 0.5 to 3 mm, and said line is held during casting at aspacing from an adjacent one of said casting surfaces within a range of0.5 to 3 mm.
 11. A casting machine according to claim 10, characterizedin that said included angle is in the range of 15 to 85 degrees.
 12. Acasting machine according to claim 10, characterized in that saidincluded angle is in the range of 15 to 80 degrees.
 13. A castingmachine according to claim 12, characterized in that said included angleis in the range of 15 to 75 degrees.
 14. A casting machine according toclaim 12, characterized in that said included angle is within the rangeof 30 to 70 degrees.
 15. A casting machine according to claim 10,characterized in that said spacing is 1±0.5 mm.
 16. A casting machineaccording to claim 12, characterized in that the tip has two of saidwalls aligned with each other with said metal-contacting inner surfacesconfronting each other across a metal-conveying channel.
 17. A castingmachine according to claim 16, characterized in that said walls of saidtip diverge from each other in a direction extending towards said outerextremity.
 18. A casting machine according to claim 17, characterized inthat said walls diverge from a longitudinal axis of the tip at an angleof about 8 degrees.
 19. A process of continuous strip casting a moltenmetal to form a cast metal strip article, which process comprisesfeeding a molten metal, which develops an oxide layer when in contactwith air, from a nozzle having a projecting nozzle tip onto at least onemoving casting surface such that the metal forms a meniscus having asurface coating of metal oxide between an extremity of the tip and thecasting surface, characterized in that said metal is fed from a tiphaving an inner surface and an end surface that interconnect at a lineand form an included angle of less than 88 degrees, said at least onewall has a thickness adjacent to said line in the range of 0.5 to 3 mm,and said line during casting is positioned at a spacing from an adjacentone of said casting surfaces within a range of 0.5 to 3 mm.
 20. Aprocess according to claim 19, characterized in that the final contactbetween the molten metal and the tip is confined to a fixed position onthe tip by providing the tip with an inner metal-contacting surface andan end surface that interconnect at a line and have an included angleselected from a range of 15 to 80 degrees, and causing the molten metalto flow over said interconnecting line onto said casting surface.